Project Summary Activation of the COX-2/mPGES-1/PGE2 signaling axis is a hallmark of many cancers, including colorectal cancer (CRC), prompting the implementation of prevention strategies targeting COX-2 activity1-3. Despite their demonstrated chemopreventive efficacy, long-term treatment with COX inhibitors poses significant health risks associated with global suppression of physiological prostanoids, including GI and cardiovascular toxicities. We have shown that targeting the downstream terminal PGE2 synthase, mPGES-1, specifically reduces inducible PGE2 formation without disrupting synthesis of other essential prostanoids4. We have also shown that abrogation of inducible PGE2 formation confers dramatic protection against colon carcinogenesis in both azoxymethane (AOM)-treated Strain A mice and Apc?14/+ mice, with or without associated DSS-induced inflammation4-6. Thus our data and the work of others point to mPGES-1 as a drugable target with potentially high chemopreventive benefit. In order to accelerate its development as a viable drug target, and to better understand the mechanisms underlying this protection, further investigation of mPGES-1 is required. In this exploratory project, we propose to examine how mPGES-1 is incorporated into intracellular signaling pathways involved in the maintenance of the mucosal barrier, and the growth and progression of cancerous lesions. Towards this end, we have recently created an mPGES-1 conditional knockout mouse (cKO) in which mPGES-1 can be inactivated in a cell type-specific manner. In the proposed studies, we will test the cell type-dependent contribution of inducible PGE2 to colon carcinogenesis in the AOM-DSS colis-associated cancer model. Our goal is to determine the relative contribution of PGE2 synthesis generated from its primary cellular sources (epithelial vs. myeloid) to colon cancer development. In Aim 1, we will inactivate mPGES-1 in epithelial cells by crossing cKO with Car1-Cre mice (cKO:Car1). Following AOM- DSS treatment, we will examine the impact of inducible epithelial-derived PGE2 on mucosal injury, repair and multi-stage CRC development. In Aim 2, we will conditionally inactivate mGES-1 in the myeloid-derived lineage, using Lyz2-Cre (cKO:Lyz2) mice and determine the impact of AOM/DSS on mucosal injury and cancer development. Endpoints analyzed in each genetic model will include neoplastic lesion formation and growth, activation status of the COX-2/mPGES-1/PGE2 signaling axis, Wnt signaling and the mutation status of Apc and CTNNB1. We will also study epithelial-stromal cross-talk with a focus on the recruitment and activation of the potent immune-suppressing Tregs and MDSC cell populations. Results from these studies will define the critical sites of inducible PGE2 formation and its relative contribution to colon carcinogenesis. In addition to providing fundamental insight into the process of CRC development, these studies will provide information for identifying patient populations that are most likely to benefit from mPGES-1 inhibition and at what stages of cancer development these inhibitors would be most effective.